mckenna



PmM. M KENNA COMPOSITION OF MATTER Filed Oct 28, 1930 March 8, 1932.

INVENTOR m /z am, WQ$WQ,

Patented Mar. 8, 1932 PHILIP M. MICKENNA OF UNITY TOWNSHIP, WESTMORELAND COUNTY, PENNSYLVANIA, ASSIGNOR TO VANADIUM ALLOYS STEEL COMPANY, OF LATROBE, PENNSYLVANIA,

A CORPORATION OF PENNSYLVANIA 'oOMrOsrr-ION or MATTER Application filedflctober 28, 1930. Serial No. 481,735.

The object of this invention is to form a material for tools, dies and like purposes which is superior to any heretofore known in metallurgical science and art.

Cutting tools have commonly been made of steel and high speed steel. Again cast alloys known as stellites have been produced for this purpose. Also cast alloys largely of such metals as tungsten, molybdenum and tantalum, with carbon and sometimes other metals and/or metalloids in minor quantities have been proposed as tool materials. Also tungsten carbide sintered with cobalt has been employed as a tool material.

I have previously produced, by means of the .new process which I have discovered, namely by high frequency welding on a microscopic scale under pressure, a composition of tantalum metal and tungsten carbide which is superior to cobalt cemented tungsten carbide compositions for steel-cutting tools.

The improved composition which is the subject matter of the present application is superior to all of the hitherto known tool materials. It is harder than hardened steel or high speed steel. The latter in their hardest condition measure about 69 on the Rockwell C scale, while my improved composition hasla hardness of 71 to 7 6 on the Rockwell C sca e.

My improved composition is superior to high speed steel in its metal-cutting ability, as it does not fail as a tool point when cutting steel of 440 Brinell hardness at speeds exceeding one hundred feet per minute, while the tools of high speed steel fail in less than thirty seconds when cutting under equal conditions.

My improved composition is superior to stellites and other known cast alloys of tungsten and carbon, either with or without other metals, as regards durability and furthermore it is free from inequalities due to crystallization and segregation inherent in all cast products which products are also usually impaired by blow holes.

My improved composition is superior to cemented tungsten carbide alloys formed by heating, in which pulverized tungsten carbide is sintered with a softer metal having a substantially lower melting point. The metal cobalt has the properties of having a. substantially lower melting point than that of the tungsten carbide. The presence of a relatively soft metal like cobalt as a binder is a disadvantage, and the percentage of such binder metal must be adjusted to give the necessary toughness or the tools will be brittle.

Thus when a wear-resisting edge is desired as low as 3% cobalt is customary, although 13% is required by the tools of sufiicient toughness for lathe work in cuttin phosphor bronze and cast iron with intermlttent cuts. With 13% of cobalt the metal will not serve as a lathe tool point for cutting hard steel, invariably showing a cratering immediately back of the edge, due to wear. Also the point wears rapidly in front destroying the clearance and cutting efliciency.

I attribute this to the tearing out of grains of tungsten carbide from the soft metal binder.

The usefulness of cobalt cemented tungsten carbide tools is thus limited not by the inherent qualities of tungsten carbide, but by the relatively weak metal cobalt.

My improved composition is superior to the composition described in my co-pending application in which tantalum metal and tungsten carbide are formed int0.a composition by my process by high induced eddy currents of electricity. The latter cuts steel without cratering, but is not tough enough to stand up cutting hardened steel with the lipped point which is essential to curl the chip and thus dispose quickly of the metal removed which is otherwise dangerously shot out in straight strips of hot and sharp cuttings, dangerous to the operators of the lathes.

This difference in toughness I attribute to the fact that tantalum metal has a cubic atomic lattice while tungsten carbide has a hexagonal lattice and thus they do not form as tough a composition as the carbide of tantalum, columbium or vanadium and tungsten metal which latter all have a cubic crystalcarbides .are vanadium carbide,

C. I employ from 30% sten and from 70% to 30% the other ingredient or "centages being atomic.

' together with a mono-carbide of a metal of the first column in the fifth of Mendeleeffs periodic table.

group of elements Such known columbium carbide and tantalum carbide.

The melting point of tungsten is 337 0 (3., of molybdenum 2620 0., while the carbides of tantalum and columbium are reportedto.

have melting points of 4100 absolute and vanadium carbide is reported to melt at 27 to 70% of the tungof the carbide of ingredients the perlVhere molybdenum replaces the tungsten in whole or in part an atomic weight of molybdenum equal to the atomic weight of the tungsten replaced either in whole or in part is used. Thus 96 parts of molybdenum would replace 18 parts of tungsten.

In the manufacture of my improved composition I use no so-called metal binder or cement having a substantially lower melting point than tungsten carbide.

.In the production of my improved compositionof matter I employ sufficient pressure and high frequency induced eddy currents of electricity of sufficient voltage and alternations per second to produce a welding action between the particles by a local surface phenomenon. The microscopic sparks produce very unusual conditions locally evidently vaporizing and re-condensing these difficult to melt metals at the surface, because the resulting composition of matter has a density actually slightly greater than the mean calculated density of the constituents.

The temperature involved is materially lower than the melting temperature of any of I the ingredients of my composition. And

C after the product is formed, 1t is an unmeltablesolid at the temperature at which it is "made. Pieces put back in the sparking chamber while other metal of the same kind is being prepared in the chamber remain unmelted, thus proving that the formed composition as well as the ingredients separately are not heated to the melting point.

For example I have produced my improved composition at a temperature materially less than the melting point of any of the ingredients namely about 2000 C. in the presence of a pressure of about 4000 pounds per square inch and high frequency induced eddy currents of electricity of about 7700 volts and as high a frequency as is reasonably attainable although 10,000 to 100,000 alternations per second may be satisfactorily employed.

.The voltage and frequency should be sufficient to produce the requisite local surface expected product which eaaaee quencies may be obtained by using a hi h frequency induction coil, with high voiage transformer, condensers of suflicient capacity and a mercury arc gap. The object in view in using such high frequency is not that of heating so much as it is to obtain a welding action between the particles of tungsten and/or molybdenum and the particles of the carbide. This high frequenc produces the sparks which are requisite or the welding action. Such interior sparln'ng cannot be obtained by the use of resistance heating by electricity.

All three conditions may be obtained in the following manner. A coil of flattened 'side diameter making twenty-six turns with the succeeding layers of the copper coil separated by a space of The coil is shellacked and suitable connections made at the ends of which water may flow through the center of the flattened copper pipe which is not flattened sufliciently to impede the flow; also electric connections are made at either ends of the coil. A fused silica tube 4- outside diameter and about 13" long with wall thickness of about is placed in the copper coil and a refractory block about 3% in diameter and 2" thick is inserted at the bottom of the silica tube, resting on a sub stantial stone block supported by steel plates. A 2 cylinder of carbon 8" long is cut out with a hole of the cross section desired in the bit of hard metal. The powdered tung sten and/or molybdenum metal and the finely divided tantalum carbide to the specified amount carefully mixed is inserted in the hole in suflicient quantity so that the resultant bit of hard metal is of the desired size calculating from the specific gravity of the will vary from 11 to 16 depending upon the proportions of. the ingredients. A ram also of carbon is fitted into the hole and a screw arranged above the ram so that a pressure of 4000 pounds per square inch may be applied by hand. The

high frequency electric current may be obtained from a transformer and condensers of sufficient capacity, or from known ways by rotary converters. The carbon mold is insulated from the silica tube by surrounding it with carbon black.

In the accompanying drawing, wherein the apparatus is illustrated in vertical section, 1 represents the mold; 2 the hole bored therein; 3 the ram; 4 the refractory .block upon which the mold rests; 5 the coil of a high frequency electric furnace; 6 the fused silica tube in which the mold assembly is packed in the carbon black insulation 7, and 8 is the material to be treated.

The induced electric eddy currents at the rate of 5 kilo volt amperes are applied and continued for twenty-five minutes, when pressure is applied to the ram, gradually in creasing to 4000 pounds, until atthe end of forty minutes the current is turned oif, the mold removed from the carbon black and allowed to cool.

On breaking the carbon mold the metal product is found tobeof great density, ab-

solute uniformity and capable of taking akeen and lipped edge on a silicon-carbide grinding wheel. Its size is close to the exact size of the mold.

These metal tips may be attached as by brazing to suitable shanks to form cutting tools. 7

Steel may be cut with these tools at speeds heretofore unattainable. Intermittent cuts a on hard steel have been made with my new tungsten is 110.4

composition, a thing impossible with cobaltcemented tungsten carbide tools.

The composition of the metal product may be-varied somewhat, but a metal comprising an atomic equivalent Weight of tungstenbr molybdenum, to a molecular equivalent weight of the mono-carbide is typical. Thus 184 parts of tungsten with 193 parts of TaC may be used. The useful limits .of the composition liebetween six tenths of .an atomic equivalent of tungsten or molybdenum to one and four tenths atomic equivalents of the same, to which a quantity of the mono carbide in molecular equivalent weight inversely varying from one and four tenths molecular equivalent weights to six tenths of an equivalent weight is added. I

Six-tenths of an atomic equivalent of parts by weight and sixtenths of an atomic equivalent of molybdenum is 57.6 parts by weight. Again one and four-tenths of an atomic equivalent of tungsten is257 .6 parts by weight and one and fourtenths of an atomic equivalent of molybdenum is 134.4 parts by weight. V

In the case of the carbide one and fourtenths of a molecular equivalent of tantalum carbide is 270 parts by weight, while sixtenths of a molecular equivalent of tantalum carbide is 115.8 parts by weight.

Thus a composition totaling 380.4 parts by weight made up of 110.4 parts by weight of tungsten and 270 parts by Weight of tantalum carbide would contain twenty-nine percent of tungsten and seventy-one percent of tantalum carbide. And again a composition totaling 378.4 parts by weight made up of 257.6 parts by weight of tungsten and 115.8 parts by weight of tantalum carbide would contain sixty-nine percent of tungsten and thirty-one about 90% Ta O makes a total of 327.6 parts by weight, of which the molybdenum is approximately seventeen and one-half percent and the tantalun}5 carbide eighty-two. and one-half percen 1 And again in the case where one and fourtenths 0 an atomic equivalent of molybdenum is substituted for a like atomic equiva lent of tungsten, the molybdenum is present in 134.4 parts by weight with 115.8 parts by Weight of tantalum carbide, making a total of 250.2-parts by weight of which the molybdenum is approximately fifty-three and three-quarters percent and the tantalum carbide forty-six and one quarter percent.

I prefer to use a mono-carbide but a small variation of say 20% in the carbon content of the carbide is not fatal to the production of a useful composition although the best com- .position corresponds closely to the'formulee of mono-carbide.

The difference between my composition and a fused alloy, is seen by the fact that a fused alloy of say 50% tungsten, 3% carbon, and the remainder tantalum, is brittle and worthless as a metal-cutting tool, while metal prepared according to my invention containing 50% IV and 50% of TaO, resulting in an average carbon content of over 3% is strong and tough enough'that it may be given a lipped or cupped cutting edge so as to curl the chip, a thing impossible heretofore with my steel-cutting composition.

In the cast alloy, for instance as described I in British Patent N 0. 270,640 by Alfred Kropf a carbon content of only .70% is advised, (page 1, line 41).

Likewise when I have melted pieces of my composition, the resulting alloy is brittle and worthless for steel cutting tools. This shows .that my composition cannot be formed by the melting process.

Instead of employing the carbide of'one metal I may employ the carbides of any two or all of the metals of the group. The carbides of the metals such as vanadium carbide I have prepared by heatin the pentoxide intimately mixed with car on, in suitable proportions in graphite crucibles at about 1900 C. in the absence of air, although known ways of preparing the carbides such as heating the oxides with ethane or other carbon containing gases may be used. For a mixture of tantalum and columbium oxides, and 10% Cb O. I use 22 72: of its weight of carbon black which produces a carbide about 6.4% C. The p'res- As an example I take tungsten metal powder, and 50% of tantalum and columbium carbide mixture, containing about 5% of CbC and 95% of TaC, running about 6.4% C and intimately mix these in a ball mill, by grinding for several days.

This very lint powder placedin the sparking char .ber and treated for forty-seven minutes at 5-kva. with induced high frequency eddy currents of 7700 volts, and pressure 0 4000 pounds per square inch results in a bit of metal composition which possesses the remarkable steel-cutting qualities desired in the commercial machining of steel. Such a product analyzes about 3.1% C and can be tested on the ordinary Rockwell diamond point hardness tester with 150 kg. load as used in testing hard steel.

This test, in the case of other forms of hard compositions, if a 150 kg. load be imposed on the penetrator will result in the penetrator being chi ped and shattered and the impression will lle irregular, which result is due to the great inequality in compression hardness between contiguous particles of the composition. Thus in the case of a cemented, that is sintered', cobalt tungsten carbide composition and also in the case of a cemented, that is sintered, product of nickel and tantalum carbide the cementing metal has a very much lower compression hardness than the other ingredient which in the one composition is tungsten carbide and in the other composition is tantalum carbide.

In the case of my improved composition the compression hardness of both ingredients is very high and of substantial uniformity j and thus the pe'netrator has no opportunity to slip or jump from a harder to a softer particle, and the impression is clean cut. The foregoing is proof of the superior toughness of my composition. a

The same test is used in measuring the toughness of nitrided steel cases.

It is well known that a composition of these high melting point metals with carbon which I has been formed by melting has a coarse crystalline fracture, and is unsuited for a tool material. By my process I avoid this crystallization and a fracture of my metal shows a fine silky conchoidal structure. This discloses a reason for the relative toughness of my composition.

I What I claim is 1. A material for cutting-tools, dies and the like, in which the particles are in welded relation to each other and which comprises a composition of from approximately seventeen and one-half percent to sixty-nine percent by weight of a metal of a group composed of tungsten and molybdenum and from approximately eighty-two and one-half percent to thirty-one percent by weight of the carbide of a metal in the first column of the fifth group of Mendeleefi"s periodic table.

by weight of f the like,

2. A material for cutting-tools, dies and the like, in which the particles are in welded relation with each other and which comprises a composition of approximately from twenty-nine percent to sixty-nine percent by weight of tungsten metal and approximately from seventy-one percent to thirty-one percent by weight of tantalum carbide.

3. A material for cutting-tools, dies and in which the particles are in welded relation with each other and which comprises approximately equal proportions by weight of a metal of a group composed of tungsten and molybdenum and of the carbide of ametal in the first column of the fifth group of Mendcleefls periodic table.

4. A material for cutting-tools, dies and the like, in which the particles are in welded relation with each other and which comprises Y approximately equal proportions by weight of tungsten metal and tantalum carbide.

Signed at Pittsburgh, Pa., this 23rd day of October, 1930. 1

PHILIP M. MGKENNA. 

